Method of spraying adhesives



Jan. 1941- R. c. BENNER ETAL 2,

' us'mon 0F srnmm ADHESIVES Filed Ma 2a, 1936 INVENTOR.

RAYMOND C. BENNER ROMIE L. MELTON BY HENRY P. KIRGHNER ATTORNEY.

Patented Jan. 21, 1941 2,229,490 METHOD OF SPRAYING ADHESIVES Raymond C.Benner, Romie L.

P. Kirchner, Niagara Falls, mesne assignments, to The pany, NiagaraFalls, Delaware Melton, and Henry N. Y., assignors, by Carborund'im Com-N. Y., a corporation of Application May 26, 1936, Serial No. 81,910

3 Claims.

This invention relates to a method of treating granular coated materialand particularly to a process for applying a sizing coat of adhesivesuch as animal or hide glue to sheet material which has been coated withabrasive granules.

Sheet abrasive material such as paper or cloth is usually formed bydepositing abrasive granules or particles on an adhesively coatedsurface of such material. The web of sheet material is first coated withan adhesive such as glue by any well known means such as applying alayer of glue to the web material by means of a roll. Earlier methods ofspreading the abrasive grain over the adhesive surface usually consistedof moving the web along below a hopper filled with abrasive grain fromwhich the abrasive particles were permitted to fall onto the adhesivesurface of the web. The falling abrasive grain in such a method iscaused to be spread evenly over the surface of the web by moving thesame at a uniform rate and substantially in the direction of the surfacethereof below the hopper. The abrasive particles spread along theadhesive coated surface of the web while evenly distributed by such amethod were nevertheless haphazardly arranged with respect to eachother. That is to say the abrasive grains were not oriented with respectto each other or the web material. Abrasive granules are often of anelongated shape and the elongated grain, by permitting the same to fallonto the adhesive, generally come to rest therein with the major axisthereof in a plane along that of the flat surface of the web material.Abrasive paper or cloth formed in such a manner presented no realproblem in applying a sizing coat to the granular surface. That is tosay the haphazardly arranged particles were easily bonded to the sheetmaterial by a simple method of applying the sizing adhesive thereto. Theadditional or sizing coat of adhesive being usually applied to theabrasive surface by means of a roll partially immersed in a gluecontainer from which the glue is carried to the abrasive coated'web.

More recently, however, methods have been devised whereby the abrasiveparticles are arranged in an oriented fashion with respect to each otherand with respect to the sheet backing material. Elongated abrasivegrains by such methods are usually projected upwardly in an orientedmanner into engagement with a layer of adhesive and carried by the underside of a moving sheet or web. The abrasive grains, by reason of theirorientation, engage the adhesive layer in such a manner that only theend portions thereof are embedded in the adhesive layer.

The sheet or web material is generally maintained in the upside downposition until the adhesive coat obtains a preliminary set and theabrasive particles are thus temporarily prevented from moving or losingthe oriented arrangement thereof along the web surface.

It will be appreciated that such an arrangement of abrasive granulesrequires an unusually well applied sizing coat of an adhesive since onlythe end portions of the abrasive particles'are embedded in the firstlayer of adhesive and therefore a relatively insecure anchorage of theabrasive particles is provided. It will also be apparent that thecustomary method of applying the sizing coat by means of a roll can notbe advantageously employed since the oriented abrasive particlestemporarily aflixed to the sheet material would be caused to move by theengaging roll and the oriented arrangement thereof would be destroyed.20

An object of the present invention is, therefore, to provide a method ofapplying a sizing coat to sheet material carrying abrasive granuleswhich will not disturb the previous arrangement of the abrasiveparticles.-

Another object of the invention is to devise a process of applying asizin coat to abrasive surfaces whereby only the base portion of theabrasive particles will be coated to securely afiix the same to a sheetbacking material, leaving the uppermost end portions substantially freeof the sizing material. V

Methods of applying a sizing coat of adhesive such as glue wherein thesame is-applied without rolling the granular surface have been devisedin the past. Such methods usually include a nozzle arrangement adjacentthe granular surface into which adhesive is forced under constantpressure and sprayed along the abrasive surface. The spraying method hasbeen successfully employed when used in connection with an adhesivehaving a relatively constant viscosity. The spraying method provides thedesired results of coating the base portion of the abrasive granules andfurnishes the adhesive to the abrasive granules in such a manner as toimprove the anchorage thereof without coating the upper portion orcutting edge. This sprayingprocess is described in considerable detailin Patent No. 2,201,194, issued May 21, 1940, to Romie L. Melton,Raymond C. Benner and Henry P. Kirchner.

The use of animal glue and particularly hide lue as a sizing coat forabrasive surfaces has been recognized as particularly desirable inproviding a good anchorage for the abrasive particles 55 and theconstant pressure method of moving such adhesive to a nozzle andspraying as a sizing substance has not been satisfactory. The diflicultyin spraying such sizing material arises from the peculiar variations inthe viscosity of the glue. The imperfect fluid nature of such a glue ishighly susceptible to changes resulting from a wide variety of causesand conditions. It has been found that the best working fluid conditionof glue is obtained by maintaining the same at a temperature ofapproximately 146 F. In one instance the glue maintained at such atemperature appears to have a certain viscosity and when tested within arelatively short period of time has been found to present a widedifference in the tendency thereof to resist movement. It appearstherefore that time alone will cause the fluid condition of animal orhide glue to change and this probably results from such causes ashydrolysis or possibly as a result of bacterial decomposition. Theaddition of new glue of substantially the same constituency to apartially consumed container of hide glue has been found to materiallyalter the viscosity of the entire batch. Small variations in the mannerin which the fluid glue is mechanicallyv agitated is known-to cause thefluid nature of the otherwise unchanged glue to be altered. For example,the precarious nature of hide glue to become less fluid during thenormal course of manipulation renders the use of compressed air or gasat a constant pressure impractical as a means for feeding a nozzle inspraying a sizing coat of such glue onto an abrasive surface since theconventional spraying apparatus often becomes clogged by the coagulatingglue. The passages of the spraying apparatus often become restricted bythe congealing of less viscous glue and an irregular application of thesizing coat results from the use of a constant pressure as a means ofprojecting the glue onto the abrasive coated material.

On the other hand, the glue may become more fluid as a result of one ormore of the above indicated causes. A constant pressure feed for suchless viscous adhesive will therefore move an excessive amount of glue tothe spray nozzles and onto the surface to be coated.

It is therefore a further object of the present invention to providemeans for projecting a stream of an adhesive such as hide glue onto anabrasive surface by a method which will furnish a uniform sizing coatirrespective of variations in the viscosity of the adhesive.

In the accompanying drawing,

Figure 1 is a diagrammatic view of apparatus for carrying out a methodof spraying granular surfaces with hide glue.

Figure 2 is an enlarged sectional view of a portion of an abrasivecoated web before the adhesive sizing coat has been applied.

Figure 3 is an enlarged section through a fragment of an abrasive coatedweb after the sizing application.

Referring to the drawing, there is shown generally at H) a number offestoons of abrasive coated web material arranged in a position topermit a proper drying or setting of the adhesive which is used toprovide a preliminary anchorage for the abrasive granules previouslyattached to and carried by a web H. The abrasive granules l2 shown inFigure 2 are attached to the flexible sheet or web by means of a layerof adhesive M. The abrasive granules are shown to be oriented to moreclearly illustrate the hereinafter described method of applying thesizing coat.

However, it will be appreciated that the present invention providesvarious advantages in applying the sizing coat of adhesive to any typeof abrasive coated sheet material. The abrasive granules |-2 may beapplied to the adhesive layer M by any suitable method and the adhesivelayer M may be allowed to obtain a set by storing the abrasive coatedweb on drying racks in a festooned fashion as indicated generally at H].

After the adhesive layer M has been properly cured or set to temporarilyamx the abrasive granules l2 to the backing material II, the web may bemoved from the racks and supported in a horizontal manner by means of aplurality of suction rolls l6 and H. The rolls l6 and I! should berotated at a constant rate of speed to move the abrasive surfaces of theweb H beneath the nozzles l8 and |9 in such a manner as to permit auniform sizing coat of adhesive to be sprayed.

thereon.

Adhesives, such as hide glue, which must be applied in a heatedcondition may be maintained in a desirable fluid state in a receptacle2| by providing a heating jacket around the outer wall 22 into which hotwater or steam may be injected through a supply line 23 to maintain thetemperature of the glue contained in the receptacle 2| at approximately146 F. An agitating device 24 is also provided and arranged to berotated within the glue receptacle 2| so that the glue may be maintainedat an even temperature and constituency throughout the entire bulkthereof.

The liquid adhesive is fed from the receptacle 2| to a constant volumepump 26 by means of pipes 21 and 28. The pump 26 is of the type whichwhen operated at a particular speed will deliver a constant or uniformvolume of liquid at the discharge end thereof. The discharge port of thepump 26 is connected. to the nozzle i8 by means of a. pipe or flexibletube 29. It is important that a pump of the constant volume character beincluded in the adhesive supplying line so that the fluid adhesive willbe furnished to the nozzle l8 at a constant rate irrespective of thechanges in the viscosity of the fluid adhesive. For instance, if thenozzle or the piping arrangement offers more resistance to the flow ofmore imperfect fluid adhesive, the pressure from the discharge port ofthe pump will build up by reason of the recurring equal volumepulsations and the more viscous adhesive will nevertheless be forcedfrom the nozzle it) at a uniform rate.

Any number of nozzles may be arranged along the surface of the web H toproperly spray the sizing coat onto the abrasive surface. It will benecessary in each case to provide a constant volume pump to supply theliquid adhesive to each additional spraying nozzle. Such'a pump 3| istherefore employed to move the liquid adhesive from the receptacle 2|through the pipe or flexible tube 32 and into the nozzle IS.

The pumps 26 and 3| may be driven by any suitable means such as by avariable speedmotor 33 appropriately belted to the two pumps. The speedof the driving device should be controllable in order that the volume ofadhesive supplied to the spraying equipment may be regulated. That is tosay the quantity of adhesive delivered by the pump will be constant fora given speed by reason of the structure of the pump but it may bedesirable to adjust and fix the speed of the pump by means of thevariable speed motor to control the rate of the constant delivery andtherefore control the amount of adhesive delivered to the sprayingnozzle and accordingly the extent of the sizing coat. It will beappreciated that the thickness or extent of the sizing coat may also becontrolled by adjusting the speed of the moving web ll. After the speedof the pump or pumps have been adjusted to provide the proper volume ofadhesive to be supplied to the nozzle or nozzles, the speed of the motor33 should be fixed and the speed of the rotating rolls I6 and .l'!should be adjusted and fixed at a uniform rate in order that the sizingcoat may be evenly and uniformly depositedalong the abrasive surface ofthe web,

In order that the liquid adhesive may be properly dispersed or atomizedduring the spraying thereof, a gaseous medium under pressure is suppliedto the nozzle or nozzles by means of pipe 35. With the particular spraynozzles used, it has been found that steam at a pressure ofapproximately 130 lbs/sq. in. is particularly adaptable for the purposeof atomizing hide glue. Compressed air has a tendency to cause hide oranimal glue to set or become chilled before it reaches the surface beingcoated and not be deposited in a suitably fluid condition. The use ofmoist steam eliminates this difiiculty since the moisture in the steamprevents evaporation of the water from the liquid glue and steam heatprevents cooling and jelling of the glue during the spraying thereof.Furthermore, the steam serves as an atomizing agent for breaking theliquid into droplets and carrying same into engagement with the baseportion of the abrasive granules.

The abrasive coated web ll, after passing the spraying equipment, iscoated with a sizing layer of adhesive as indicated in Figure 3, It isto be noted that the spraying of adhesive onto the abrasive surfacedrives the liquid adhesive to the base portion of the abrasive granulesleaving the tips or cutting portion thereof free of the adhesivecoating. The spraying method in addition to rendering the cuttingportion v of abrasive granules uncoated also forces the adhesive to aposition at the base of the particles to firmly bond the same to the webbacking material. The adhesive is projected from the nozzles at a.rather high velocity so that the sizing coat of adhesive 36 is forcedbetween the abrasive granules l2 in such a manner that the layer isconsiderably thinner at a midpoint between the grains and the force ofthe sprayed droplets causes the glue to extend upwardly along thegranules to further provide an im proved anchorage thereof. i

While the present method of employing a constant volume pump has beendescribed as being particularly advantageous in spraying glue onto agranular coated surface, it will nevertheless be apparent that otherliquid adhesives which are subject to changes in viscosity such as heathardenableor phenolic resins are equally adaptable to the presentmethod.

We claim:

1. The method of applying a layer of glue to an abrasive coated webcomprising the steps of preparing a heated solution of animal glue, saidglue being of such character that the viscosity changes appreciablyunder normal conditions, continually pumping a constant volume of saidglue to a spray nozzle irrespective of any changes "in viscositythereof, atomizing and projecting a uniform layer of a predeterminedquantity of said glue onto the abrasive coated web.

2. The method of applying a. layer of sizing adhesive to an abrasivecoated web comprising the steps of preparing a liquid adhesive, saidadhesive being of a type which does not re main constant as toviscosity, continually pumping a constant volume of said adhesive to aspray nozzle irrespective of any changes in' viscosity and spraying auniform layer of said adhesive onto the abrasive coated surface.

3. The method of manufacturing coated materials which comprises bringingan adhesive to a fluid state, said adhesive being of such character thatthe viscosity changes appreciably under normal conditions, continuallymoving a constant volume of the fluid adhesive to a nozzle irrespectiveof any changes in viscosity and applying a uniform layer of saidadhesive to the surface being coated.

- RAYMOND C. BENNER.

ROMJE L. MELTON.

HENRY P. KIRCHNER.

